The overall objectives of this project are to investigate cellular and genetic mechanisms in the induction and regulation of murine cell-mediated immune responses to alloantigens in vitro. The work is focused on the function of alloantigen-activated murine suppressor T cells in the control of mixed leukocyte reactions and the generation of cytotoxic T lymphocytes. Cell surface features of T lymphocytes producing and responding to molecules elaborated in the regulation of in vitro cell-mediated immune responses will be studied in detail. An additional aspect of this work is to identify and characterize genetic loci that can induce such responses both within and adjacent to but outside the H-2 complex. Cell-mediated immune responses to antigens encoded in the Qa-T1a region are of particular interest. Regulatory interactions between cellular subpopulations involved both in the induction and regulation of these responses will be explored. The relationship of antigens recognized serologically and by T cell-mediated cytotoxicity will also be investigated.